Rename AbstractXdsClient to ControlPlaneClient (#9934)

AbstractXdsClient is not abstract.
diff --git a/xds/src/main/java/io/grpc/xds/AbstractXdsClient.java b/xds/src/main/java/io/grpc/xds/ControlPlaneClient.java
similarity index 98%
rename from xds/src/main/java/io/grpc/xds/AbstractXdsClient.java
rename to xds/src/main/java/io/grpc/xds/ControlPlaneClient.java
index 57e0575..5a3400c 100644
--- a/xds/src/main/java/io/grpc/xds/AbstractXdsClient.java
+++ b/xds/src/main/java/io/grpc/xds/ControlPlaneClient.java
@@ -60,7 +60,7 @@
  * Common base type for XdsClient implementations, which encapsulates the layer abstraction of
  * the xDS RPC stream.
  */
-final class AbstractXdsClient {
+final class ControlPlaneClient {
 
   public static final String CLOSED_BY_SERVER = "Closed by server";
   private final SynchronizationContext syncContext;
@@ -92,7 +92,7 @@
 
   /** An entity that manages ADS RPCs over a single channel. */
   // TODO: rename to XdsChannel
-  AbstractXdsClient(
+  ControlPlaneClient(
       XdsChannelFactory xdsChannelFactory,
       ServerInfo serverInfo,
       Node bootstrapNode,
@@ -388,7 +388,7 @@
 
         @Override
         public void beforeStart(ClientCallStreamObserver<DiscoveryRequest> requestStream) {
-          requestStream.setOnReadyHandler(AbstractXdsClient.this::readyHandler);
+          requestStream.setOnReadyHandler(ControlPlaneClient.this::readyHandler);
         }
 
         @Override
diff --git a/xds/src/main/java/io/grpc/xds/XdsClientImpl.java b/xds/src/main/java/io/grpc/xds/XdsClientImpl.java
index af5fb5d..0216296 100644
--- a/xds/src/main/java/io/grpc/xds/XdsClientImpl.java
+++ b/xds/src/main/java/io/grpc/xds/XdsClientImpl.java
@@ -93,7 +93,7 @@
   private final FilterRegistry filterRegistry = FilterRegistry.getDefaultRegistry();
   private final LoadBalancerRegistry loadBalancerRegistry
       = LoadBalancerRegistry.getDefaultRegistry();
-  private final Map<ServerInfo, AbstractXdsClient> serverChannelMap = new HashMap<>();
+  private final Map<ServerInfo, ControlPlaneClient> serverChannelMap = new HashMap<>();
   private final Map<XdsResourceType<? extends ResourceUpdate>,
       Map<String, ResourceSubscriber<? extends ResourceUpdate>>>
       resourceSubscribers = new HashMap<>();
@@ -144,7 +144,7 @@
     if (serverChannelMap.containsKey(serverInfo)) {
       return;
     }
-    AbstractXdsClient xdsChannel = new AbstractXdsClient(
+    ControlPlaneClient xdsChannel = new ControlPlaneClient(
         xdsChannelFactory,
         serverInfo,
         bootstrapInfo.node(),
@@ -218,7 +218,7 @@
               return;
             }
             isShutdown = true;
-            for (AbstractXdsClient xdsChannel : serverChannelMap.values()) {
+            for (ControlPlaneClient xdsChannel : serverChannelMap.values()) {
               xdsChannel.shutdown();
             }
             if (reportingLoad) {
@@ -490,7 +490,7 @@
    */
   private final class ResourceSubscriber<T extends ResourceUpdate> {
     @Nullable private final ServerInfo serverInfo;
-    @Nullable private final AbstractXdsClient xdsChannel;
+    @Nullable private final ControlPlaneClient xdsChannel;
     private final XdsResourceType<T> type;
     private final String resource;
     private final Set<ResourceWatcher<T>> watchers = new HashSet<>();
@@ -518,7 +518,7 @@
       // is created but not yet requested because the client is in backoff.
       this.metadata = ResourceMetadata.newResourceMetadataUnknown();
 
-      AbstractXdsClient xdsChannelTemp = null;
+      ControlPlaneClient xdsChannelTemp = null;
       try {
         maybeCreateXdsChannelWithLrs(serverInfo);
         xdsChannelTemp = serverChannelMap.get(serverInfo);
diff --git a/xds/src/test/java/io/grpc/xds/XdsClientImplTestBase.java b/xds/src/test/java/io/grpc/xds/XdsClientImplTestBase.java
index 0f18d3d..23364bb 100644
--- a/xds/src/test/java/io/grpc/xds/XdsClientImplTestBase.java
+++ b/xds/src/test/java/io/grpc/xds/XdsClientImplTestBase.java
@@ -158,7 +158,7 @@
       new FakeClock.TaskFilter() {
         @Override
         public boolean shouldAccept(Runnable command) {
-          return command.toString().contains(AbstractXdsClient.RpcRetryTask.class.getSimpleName());
+          return command.toString().contains(ControlPlaneClient.RpcRetryTask.class.getSimpleName());
         }
       };